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Avalanche Forecast

Archived

Jan 10th, 2021–Jan 11th, 2021

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Columbia.

A bit of new snow with strong wind will keep upper elevation wind slabs fresh on Monday. They will likely be thin but reactive, especially to human triggers.

Confidence

High - The number, quality, or consistency of field observations is good, and supports our confidence.

Weather Forecast

Sunday night: Flurries, trace, light to moderate southwest wind, freezing level valley bottom.

Monday: Flurries, up to 5 cm, strong southwest wind, alpine high -6, freezing level 900 m.

Tuesday: Flurries, up to 5 cm, strong southwest wind, alpine high -6, freezing level 900 m.

Wednesday: Snow, 10-20 cm, strong southwest wind, alpine high -3, freezing level 1200 m.

Avalanche Summary

A few reports of mostly minor solar triggered avalanches came in Saturday afternoon, mostly less than size 1 but up to size 2. 

Some cornice control work was conducted across the region Saturday. Explosives produced a size 1.5 cornice which did not trigger a heavily skied slope below. A vehicle-triggered cornice drop tested a north facing alpine slope below, triggering a size 2 wind slab which did not step down to deeper layers.

Snowpack Summary

Small amounts of new snow fall on surface hoar in many areas and a thin crust on solar aspects. Previous moderate to strong winds have created variable wind effect at wind exposed elevations. 

A couple of persistent weak layers exist in the upper to mid snowpack:

  • The upper layer, found 40-80 cm down, is a spotty layer of surface hoar at treeline and below. 
  • The lower layer, found 90-150 cm down, is widespread and can present as surface hoar and/or a crust.

Avalanche activity on these layers has dwindled since last week and snowpack tests results have been moderate to hard planar, but still showing some propagation. Incoming snowfall in the forecast for this week will add additional load to these layers and may shed some light on whether they will remain a concern.

Terrain and Travel

  • Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.